Antenna coupling device



, B. ALBRIGHT ANTENNA COUPLING DEVICE Filed April 8, 1955 Aug. 11, 1936.

Patented Aug. 11, 1936 UNITED STAT earner @FFEQE' ANTENNA COUPLINGvv DEVICE Robert B. A'lbright, Philadelphia, Pa., assignor to Philco Radio & Television Corporation, Phila delphia, Pa., a corporation of Delaware Application April 8, 1935, Serial No. 15,333

9 Claims.

- receivers having improved image frequency suppression characteristics.

Another object of the invention is to provide an improved filter device in a multi-band radio receiver.

Af-urther object of the invention is to provide a superheterodyne receiver novel means for suppressing image frequencies within a certain frequency band. or. range when the receiver is adjusted to receive waves in other frequency bands.

These and other objects. of the invention will be set forth more fully in the following detailed description and pointed out particularly in the claims. The invention may be more clearly understoodv by reference to the accompanying drawing, the single figure of which is a diagrammatic illustration of a simple embodiment of the invention, it being understood that this illustration does not limit the invention but is merely for the purpose of disclosing the same.

Referring to the drawing, the antenna may be connected to ground through the series-connectedcoils L1 and L4 whichmay be shunted by another coil L2, depending upon the position of the switch S1. When the switch is in position A, the coils L1 and L4 are shunted by the coil L2 and when the switch is in the position B, the coil L2. is not only short-circuited but is also removed from the circuit by having both of its extremities connected directly to ground for reasons which will appear hereinafter. The coil L1 has distributed capacity, as indicated by the broken-line representation and this coil may have a resonant period or frequency in a frequency band or range which itis desired to suppress, for example, a band comprising relatively high frequencies or short waves. Condenser C1 may have small capacity as compared with the tuning condenser VCL. The. coil Li may be a high impedance coil, while the coil L2 may be one of less impedance than coil L4. The coil L2 may be loosely inductively coupled to the coil L2. and these coils may alsobecoupl'ed capacitively by means of the condenser C1,. which may be obtained by proper positioning of coils L2 and L3 or the conductors associated therewith. Coil L4 may be loosely inductively coupled to coil*L5. The condenser C2 is a D. C. blocking condenser and may be of such size as. to present extremely low impedance to signals of the frequency which it is desired to receive.

The serially-connected COiISLs and L5 may be tuned to the particular signal frequency which it is desired to receive by means of the variable condenser VC and the wave-band of this circuit may be changed from the low frequency or long-wave band to the high frequency or. short- Wave band by short-circuiting coil L5 by means of the wave-band switch S2. This switch also has two positions A and B, which correspond to the similarly designated positions of switch S1 10 but in position B the switch is merely open-circuited. The two switches may be combined in a single unit or may be adapted for unitary control, as indicated by the broken-line representation.

tion AA, the device is adapted to receive signals of higher frequency or shorter wave length than when the switches are in the position BB'. When the device is used in aradio receiver of the superheterodyne type, it is preferable that the intermediate frequency be between the frequencies of the high and low frequency bands which the device is adapted to receive for reasons which willappearpresently. In a particular. illustration, the high frequency or shortwave band may be the usual broadcast band in the frequency range 550 to 1540' kilocycles and the. low frequency or long-wave band may be from I50 to 350' kilocycles. It will be understood; however, that the invention is not limitedto these frequencies but applies equally to other frequency bands. In this case, the device may be adapted to suppress image frequencies in the, short-wave band whenever signals in the 35 long-wave band are being received.

The device functions to reject or suppress image frequencies in the following manner:- When the switches S1 and S2 are in the position BB', that is when the device'is a'dapted't'o receive low. frequency or long-wave signals, itis desirable to suppress any signals on the antenna of frequency within the high frequency or shortwave band. This is especially important when the high. frequency or short-wave band includes the commercial broadcast band and the powerful commercialstations found therein. Suppression of signals in the high frequency or short-wave range is. obtained by virtue of the broad resonance of coil L1, which makes this coil a very high impedance as compared with coil L4 for the undesired signals within they said range. Coils L1 and L; are in series, but only coil. L4 is coupled to the secondary circuit. The suppression of the undesired signals is further enhanced by. the

When the'switches S1 and S2 are in the posi- 15 complete removal of undesired coupling which is effected by the grounding of both ends of coil L2 and the grounding of the movable arm of switch S1, whereby capacitive coupling of the antenna with the coil L2 is eliminated. For signals in the low frequency or long-wave band which it is desired to receive, coil L1 is of low impedance as compared with coil L4.

By wayof illustration, the frequency band 150 to 350 kilocycles may be chosen as the low frequency or long-wave band. If now an intermediate frequency of 460 kilocyoles is chosen, then for a signal of frequency 150 kilocycles, it will be necessary to use a locally generated signal of 460 plus 150 or 610 kilocycles as the oscillator signal in the first detector tube in the manner well known in superheterodyne receiver practice. However, a signal of 610 plus 460 or 1070 kilocycles would also combine to produce an undesirable intermediate frequency signal of 460 kilocycles. Moreover, by virtue of the second harmonic of the oscillator frequency, the frequency of which harmonic is 1220 kilocycles, a signal of 1220 minus 460 or 760 kilocycles would also produce an intermediate frequency of 460 kilocycles.

For a signal of 350 kilocycles, at the opposite end of the range chosen, an oscillator frequency of 810 kilocycles will be used to produce the desired intermediate frequency of 460 kilocycles. A signal of 810 plus 460 or 1270 kilocycles would likewise produce an undesirable intermediate frequency signal of 460 kilocycles.

It will be seen from the above that it is desirable to suppress image frequency signals in the range 760 to 1270 kilocycles which lies within the high frequency or short-wave band chosen above as the usual broadcast band. In order to effect the desired image suppression within the stated range, the coil L1 may have a natural resonance period of approximately 1000 kilocycles and may be broadly resonant over the range 760 to 1270 kilocycles. Thus when the device is adapted for reception of the low frequency or long-wave band by virtue of the switches S1 and S2 being in the position 3-3, the coil L2 is effectively removed from the circuit as above shown and the only coupling between the antenna and the tuned circuit L3, L5, V is the inductive coupling between coils L4 and L5. Since the coil L1 serves to suppress image frequencies 'within the high frequency band, such image frequencies will be prevented from being transferred into the system. At the same time, the coil L1 presents relatively low impedance to the low frequency 'or long-wave signals which it is desired to receive and these signals are conducted into the system through the inductive coupling of coils L4 and L5.

A further advantage accruing from the device is that the condenser C1 serves as a pad for the tuning condenser VC when the switch S1 is in position B, that is, when the low frequency or long-wave band is being received. It will be seen that the condenser C1 is then connected in parallel with condenser VC, through condenser C2, and that when the switch S1 is in position A, condenser C1 is effectively in series with coil L2, and acts as a coupling impedance only. This additional functioning of C1 as a padding condenser, which results from the invention, facilitates tuning of the circuit during long-wave band reception.

When the device is adapted for reception in the high frequency or short-wave band, that is when the switches S1 and S2 are in the position A-A, the coil L2 is in shunt relation with coils L1 and L4 and. the coil L5 is short-circuite'd. The antenna is, therefore, coupled to the system only through inductive and capacitive coupling between the coils L2 and L3. The impedance of coil L2 will be small compared with that of coils L1 and L4, since coil L1 is resonant in this frequency band and coil L4 is of greaterimpedance than coil L2. Furthermore, the combination of coils L1 and L4 shunting coil L2, with the antenna capacity may be adjusted to be resonant to a frequency just below the lowest frequency of the short-wave band by which uniformity of gain may be enhanced.

Image rejection in this frequency band occurs by virtue of the location of the intermediate frequency. For example, for a signal of 600 kilocycles, the oscillator frequency is 600 plus 460 or 1060 kilocycles and the image of this signal is 1060 plus 460 or 1520 kilocycles. Likewise, a signal of 1500 kilocycles will have an image of 2420 kilocycles. Such broadcast stations as occur in this region are generally less powerful than commercial broadcast stations and, therefore, suflicient image rejection may be obtained by the tuned circuit L3 VC. 'However, if desired, a parallel tuned trap, such as an inductance with distributed capacity tuned broadly to the region 1520 to 2420 kilocycles may be inserted between the antenna and the coil L2 to provide image suppression in this region.

This invention may be used in the antenna circuit or between stages operating at the incoming frequency or at any other point where the described frequency discriminating features would be advantageous.

It will be seen from the above description that the invention provides novel and useful features in a multi-band radio receiver and particularly in a receiver of the superheterodyne type. Although the invention has been described with reference to a simple embodiment, it will be understood that various changes and modifications are possible.

I claim:

1. In a multi-band radio receiver, an antenna circuit, means in said circuit for suppressing waves in a certain frequency band, means including a coil for receiving waves'in said'fre-' quency band, means including another coil seri-'- ally connected to said suppression means for receiving waves in another frequency band, means for connecting said first coil to the antenna circuit in shunt relation to said wave suppression means and for simultaneously rendering ineffective said second coil, and means forrendering said first coil ineffective and for simultaneously rendering said second coil effective.

2. In a radio receiver, a primary circuit, means in said circuit for suppressing transfer of waves in a certain frequency band, a primary'coil in said circuit for receiving waves in another frequency band, a secondary coil inductively associated with said primary coil, means for short! circuiting said secondary coil at will, a third coil for receiving waves in said certain frequency band, means for connecting said third coil at will to said primary circuit in shunt relation to said wave suppression means and said primary coil, means for short-circuiting said third coil at will, and means for jointly controlling said connecting means and said short-circuiting means.

3. In a multi-band radio receiving circuit; an input circuit; an output circuit; means includgoecgsre:

ing a secondary winding,'.' a" condenser and ing signals in one of said frequency bands, said primary. circuit includingia primary winding inductively related to said secondary winding and a serially connected impedance presenting a high impedance to signals having frequencies in another of said frequency bands; a second primary circuit for receiving signals in said other frequency band, said second primary circuit including an impedance coupled to said output circuit; and switching means for connecting said second primary circuit in shunt relation with said first primary circuit for reception of signals in said other frequency band and for rendering said second primary circuit ineffective for reception of signals in said first-mentioned frequency band.

4. In a multi-band radio receiving circuit; an input circuit; an output circuit; means, including a secondary winding, a condenser and switching means, for tuning said output circuit over a plurality of frequency bands; a primary circuit connected to said input circuit for receiving signals in one of said frequency bands, said primary circuit including a primary winding inductively related to said secondary winding and. a serially connected impedance presenting a high impedance to signals having frequencies in another of said frequency bands; a second primary circuit for receiving signals in said other frequency band, said second primary circuit including a second primary winding associated with said secondary winding and having a lower impedance than said first primary winding; and switching means for connecting said second primary circuit in shunt relation with said first primary circuit for reception of signals in said other frequency band and for rendering said second primary circuit ineffective for reception of signals in said first-mentioned frequency band.

5. In a multi-band radio receiving circuit; an input circuit; an output circuit; means, including a secondary winding, a condenser and switching means, for tuning said output circuit over a plurality of frequency bands; a primary circuit connected to said input circuit for receiving signals in one of said frequency bands, said primary circuit including a primary winding inductively related to said secondary winding and a serially connected impedance presenting a high impedance to signals having frequencies in another of said frequency bands; a second primary circuit for receiving signals in said other frequency band, said second primary circuit including a second primary winding inductively related to said secondary winding and having a lower impedance than said first primary winding; and switching means for connecting said second primary circuit in shunt relation with said first primary circuit for reception of signals in said other frequency band and for rendering said second primary circuit ineffective for reception of signals in said firstmentioned frequency band.

6. In a multi-band radio receiving circuit; an input circuit; an output circuit; means, including a secondary winding, a condenser and switching means, for tuning said output circuit over a plurality of frequency bands; a primary circuit connected to said input circuit for receiving signals in one of said frequency bands,

said primary circuitzincluding asp'riimaryqwinding' inductivelyrelate'd: tosaidlsecondary windingfand' a:serially connected impedance presenting. a high impedance; tOISigl'lBilSi having: frequencies; in; another of said;frequencylbands;- asecond priimaryrcircuit for: receiving: signalsin. said other frequency band, said second primary circuit including a second primary winding having a lower impedance than said first primary winding; a capacitive coupling means between said second primary winding and said secondary winding; and switching means for connecting said second primary circuit in shunt relation with said first primary circuit for reception of signals in said other frequency band and for rendering said second primary circuit ineffective for reception of signals in said first-mentioned frequency band.

7. In a multi-band radio receiving circuit; an input circuit; an output circuit; means, including a secondary winding, a condenser and switching means, for tuning said output circuit over a plurality of frequency bands; a primary circuit connected to said input circuit for receiving signals in one of said frequency bands, said primary circuit including a primary winding inductively related to said secondary winding and a serially connected inductance having some distributed capacitance such that the inductance is broadly parallel resonant to frequencies in a higher one of said frequency bands; a second primary circuit for receiving signals in said higher frequency band, said second primary circuit including an impedance coupled to said output circuit; and switching means for connecting said second primary circuit in shunt relation with said first primary circuit for reception of signals in said higher frequency band and for rendering said second primary circuit ineffective for reception of signals in said first-mentioned frequency band.

8. In a multi-band radio receiving circuit; an input circuit; an output circuit; means, including a secondary winding, a condenser and switching means, for tuning said output circuit over a plurality of frequency bands; a primary circuit connected to said input circuit for receiving signals in one of said frequency bands, said primary circuit including a primary winding inductively related to said secondary winding and a serially connected impedance presenting a high impedance to signals having frequencies in another of said frequency bands; a second primary circuit for receiving signals in said other frequency band, said second primary circuit including a second primary winding having a lower impedance than said first primary winding; a variable capacitance connected to one end of said second primary winding and to said secondary winding; and switching means for connecting said second primary circuit in shunt relation with said first primary circuit for reception of signals in said other frequency band, and for rendering said second primary circuit ineffective for reception of signals in said first-mentioned frequency band and connecting said variable condenser across at least part of said secondary winding.

9. In a radio receiver including a signal transfer circuit, an output circuit for said transfer circuit comprising a secondary winding and a condenser adapted to tune said output circuit over a predetermined frequency band, and an input circuit for said transfer circuit comprissecondary winding. and a serially connected inductance having distributed capacitance, said inductance being broadly parallel resonant to a. frequency band different from and of greater 5 band width than said first frequency band, the impedance of said inductance being substantially greater than the impedance of said primary winding for signals in said second frequency band and less than the impedance of said. pri-V mary winding for signals in said first frequency band v i :7 v ROBERT B. ALBRIGHT. 

